Well known in the art is a so-called twin roll continuous casting apparatus in which a pair of internally cooled rolls having respectively horizontal axes and rotating in opposite direction to each other are disposed parallel to each other with an appropriate gap therebetween, a pool of molten metal is formed on the circumferential surfaces (the upper halves cylindrical surfaces in the axial directions) of the rolls above the gap and the molten metal is continuously cast into a metal strip through the gap while being cooled by the circumferential surfaces of the rotating rolls. There has also been proposed such a twin roll continuous apparatus applied to a case of continuous casting of steel to produce a steel strip directly from molten steel.
When a metal strip is continuosly cast through a gap between a pair of rolls, it is necessary to form a pool of molten metal on the circumferential surfaces of the pair of rolls above the gap therebetween and to maintain a level of the molten metal in the pool substantially constant by continuously pouring the molten metal into the pool. In order to form the pool of molten metal, there are required a pair of dams having their surfaces perpendicular to the roll axes which prevent an overflow of molten metal along the roll axes on the circumferential surfaces of the rolls. These dams also serve usually to regulate the width of the cast strip and are referred to herein as "side dams". In addition to the side dams disposed at the left and right sides of the rolls, a pair of front and rear dams (which may be referred to as "longitudinal dams") having their surfaces along the roll axes may be erected orthogonally to the side dams on the circumferential surfaces of the rolls so as to form a box-like pool for molten metal with the side dams and the front and rear dams.
There are known, as the pair of side dams, movable side dams which urge a pair of endless metal belts, caterpillars and the like against both edge surfaces of the rolls (side surfaces of the rolls perpendicular to the roll axes) at a location of the roll gap and move at a speed corresponding to the casting speed. With such movable side dams, however, the constitution of the apparatus becomes complicated. Also known in the art are fixed side dams which have plate-like bodies of refractories fixed to left and right side surfaces of the rolls. Since the fixed side dams undergo a great deal of friction with the rotating rolls and the ends of the strip being cast, they are generally made of heat resistant refractory materials having high strength. Never-the-less, damages of the fixed side dams are not completely avoided, may be a cause of leakage of molten metal and may invite cracks at the ends of the strip.
In Japanese Patent Application No. 62-84,555 (published as JP A-63-252,646, corresponding to U.S. Pat. No. 4,811,780), we have proposed a continuous casting apparatus for metal strip which may be said "abradable dam system" or "semi-movable dam system" intermediate between "movable" and "fixed" dam systems. According to our prior proposal, a refractory material capable of being well abraded is used as the material for the side dams, contrary to the prior art concept that refractory materials suitable for the side dams should have a good wear resistance and the highest possible strength. The abradable side dams are forcibly fed or moved in the casting direction during the casting while being frictionally abraded by slidably contacting surfaces of the rotating rolls and ends of the strip being cast. By this abradable dam system, the problems associated with the twin roll continuous casting apparatus, of molten metal leakage in the vicinity of the side dams, damages of the side dams and cracks of the ends of the cast strip are overcome, whereby the production of metal strips of a good quality may be stably carried out.